1. Field of the Invention
The present invention relates to a photosensitive member comprising a surface protective layer on a monolayer construction of selenium-arsenic alloy or a laminate-layer construction of selenium-tellurium alloy.
2. Description of the Prior Art
Remarkable developments have continued to be made in the application of electrophotographic techniques since the invention of the Carlson process. Various materials have also been developed for use in electrophotographic photosensitive members.
Conventional photoconductive materials chiefly include inorganic compounds such as selenium, selenium-arsenic, selenium-tellurium, cadmium sulfide, zinc oxide, amorphous silicon, and organic compounds such as polyvinylcarbazole, metal phthalocyanine, dis-azo pigments, tris-azo pigments, perillene, triphenylmethanes, triphenylamines, hydrazones, styryl compounds, pyrazolines, oxazoles, oxydiazoles and the like.
The trend toward increasing volumes of information in a variety of fields has been remarkable in recent years and it has become necessary to develop high speed electrophotographic systems in order to duplicate high-volume information in a short time. High-sensitivity photoconductive materials are required in such high-speed copy systems, and among the aforementioned compounds, photosensitive members composed of selenium-arsenic alloys (hereinafter referred to as Se-As) are the most physically sensitive in spectral luminous efficiency with many compounds finding practical applications. Other compounds have various inadequacies in regard to sensitivity and have not been adapted for use in high-speed copy systems.
Laser beam printers using semiconducting laser beams as a light source have become practical in recent years accompanying the remarkable developments in digital image processing technology, and these systems also need increased speed. An ideal photosensitive member having satisfactory sensitivity for the light emission wavelengths of semiconductor lasers is a so-called selenium-tellurium (hereinafter referred to as Se-Te) member comprising, from among the aforementioned compounds, a selenium layer having a selenium-tellurium layer laminated thereon.
However, conventional Se-As and Se-Te photosensitive members in common use have the following disadvantages. One disadvantage is that they are harmful to the human body. Although it is nearly impossible for the photosensitive member to come into direct contact with the human body, when such a photosensitive member is used in a copy machine, powder from said member adheres to the copy image due to surface friction caused by the member rubbing against the copy paper, cleaning materials, developer or other matter, and the powder is then discharged from the machine. Accordingly, when the copy is picked up by hand the person is directly contaminated by the selenium, arsenic and tellurium, the harmfulness of said substances being a matter for concern. Another disadvantage is poor durability. The surface hardness of Se-As and Se-Te photosensitive members barely meets the H level of the JIS standards for pencil lead hardness; consequently, the surface is readily damaged when friction is generated during use of the machine as described previously, or repeated harsh surface contact is made during paper jams and the resultant reversion to manual remedies. This damage markedly reduces the image quality due to so-called whiteouts on the copy image, and shortens the useful life span of the photosensitive material. Although the useful life span of the photosensitive member varies according to the design of the copy machine within which it is incorporated, it should normally be good for 100,000 copies. In high-speed, high-volume copy machines, a short useful life span necessitates replacement of the photosensitive member or frequent maintenance, resulting in a reduction in the efficient use of the copy machine.
In order to eliminate these disadvantages, the surface of the Se-As or Se-Te photosensitive member is covered with a protective layer, thus avoiding direct contact between the photosensitive layer and the copy paper and preventing harmful material from being discharged from the machine. Moreover, using a hard film on said protective layer is an effective method for improving wear and abrasion resistance.
Not all film material can be used to cover the surface of the Se-As or Se-Te photo-sensitive member; film material which fulfills all the following criteria must be used, and new contributions are required for the film material as well as the film-forming means.
Firstly, a film is required which can fully guarantee the amount of incident light to the Se-As or Se-Te photosensitive member, and which is capable of utilizing the high sensitivity of these photosensitive members. Secondly, a hard film is required which will not receive damage to its surface when it is put to actual use in a copy machine. Thirdly, a film is required which has superior adhesive properties in regard to adhesion to the Se-As or Se-Te photosensitive member, and which will not separate from said photosensitive member due to mechanical forces or changes in temperature or humidity when put to actual use in a copy machine. Fourthly, the film must be made of harmless materials. Fifthly, a film is required which does not have an electrical consistency superior to that of the Se-As or Se-Te photosensitive member, does not produce a residual electric potential or a so-called memory image wherein a previous image is formed over a subsequent image as either a positive or negative image during the multiple copy process, and which does not participate in the production of so-called image drift induced by charge drift on a mismatching interface. Sixthly, the film must not cause a loss of image quality or produce so-called image drift when the copy machine is in actual use or under environmental conditions of high temperature and humidity.
From these perspectives, many film materials as well as film-forming means related to surface protective layers for not only Se-As and Se-Te photosensitive members but also selenium series photosensitive members have been disclosed, thus becoming an important field of electrophotographic technology.
One means for forming the protective layer is the application method. For example, Unexamined Japanese Patent Publication No. Sho 50-30526 discloses a polyurethane overcoat layer of a 0.5 to 2.5 .mu.m thickness applied or sprayed on the surface of a photo-sensitive member of a CdSSe and ZnO compound. Unexamined Japanese Patent Publications Nos. Sho 53-23636 and Sho 53-111734 disclose photosensitive members having a specific silicide applied on selenium, selenium-tellurium alloy, and selenium-cadmium alloy photoconductive layers and hardened to form an insulating layer. Unexamined Japanese Patent Publication No. Sho 54-115134 discloses a photosensitive member having a selenium photoconductive layer formed on a substrate except at both ends, said selenium photoconductive layer having only a resin layer formed thereon by immersion application and hardening.
These disclosures attempt to resolve the aforesaid disadvantages by applying and hardening organic compounds to the surface of a selenium series photosensitive member, as do similar disclosures in Unexamined Japanese Patent Publications Nos. Sho 57-64239, Sho 58-139154 and Sho 60-101541.
In recent years another method has been experimentally applied to vacuum film formation by the glow discharge process. For example, Unexamined Japanese Patent Publication No. Sho 59-58437 discloses a photosensitive member having an amorphous Si:N or Si:O layer of 50 angstroms to 2 .mu.m in thickness formed on a selenium-arsenic alloy layer by the glow discharge process using silane gas and ammonia gas, or silane gas and nitrous oxide gas as starting materials. Unexamined Japanese Patent Publication No. Sho 60-249155 discloses a photosensitive member having an amorphous carbon or hard carbon layer of 0.05 to 5 .mu.m thickness formed on a photosensitive layer by a glow discharge process using methane or acetylene as the starting materials.
In these publications, however, there is no disclosure of any means for resolving the basic disadvantages inherent in the aforementioned Se-As and Se-Te photosensitive members.